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Bolt and Torque Recommendations for EVE 280AH LiFePo4 cells

apctjb

apctjb

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No doubt it's been covered in previous threads (quick search no results)...

What is the bolt size and material (stainless, plated, AL, ...), and recommended torque settings for tightening bus bars on the the Eve 280 cells? Are folks using any type of anti corrosion coating on the the threads?

Thanks
 
There is some info in this thread.

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280ah Lifepo4 Leisure Battery - Build Thread

All tidied up and placed into a box. Just waiting for some cables so i can rum battery Terminal to box terminals! Where did you get the box please mate?
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There are some spec sheets on page 21 of this thread.

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Xuba Electronics: DEAL - 280AH LiFePo4 cells. Purchase & Review

HEADS UP ALERT - MARCH 30-2020 I have been talking with Amy as she sent me an urgent message. The NEW BULK Order of 280AH cells has arrived at their warehouse on Saturday Evening,. Our new batch of 280AH has arrived on Saturday night. On Monday, I will send messages one by one to the clients...
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Torque etc info can be found above.
A note on using noalox or similar. That is used on the surfaces between the cell contact face & busbar, not on the bolt threads. Only a very thin coating is used, no gobs of the stuff. The bolts & busbars as supplied by the various vendor can be different, usually, the busbars are copper (sometimes tin plated which is better) with stainless screws or bolts. If you get tin plated bus bars then you don't need noalox, obviously.

My xuba 280AH cells came with 2mm thick busbars and stainless screws, the screws were too long for the thickness of busbar. That was fine as I made 4mm thick busbars with 110 copper stock and that worked out fine. If ordering from Xuba or Luyan ask for double the bus bars. If your building a "block" pack the length of the busbars is too short to go across the back pair of cells. See example below.

24v-8s-packs-png.19154
 
Here is what I found;
The internal screw with size M6 is used in the poles. The anti-torsion of pole is 8Nm. The torsion should be less than 8Nm when used. The effective thread hole depth is 6mm.
Click to expand...

The screws that came with mine are 10mm (plated steel, not stainless) and as @Steve mentioned are 2MM long when using a single busbar (2mm x 15mm bar). I requested double bars but unfortunately I did not received enough bars for my configuration. (2P16S). (Amy is going to send me additional bars.)

Question; while I am waiting (ugh...) for the busbars should I order stainless M6 screws and should I coat the treads as the battery terminals are Aluminum and the bolts steel (plated or stainless).??

My understanding is a 2MM x 15MM busbar has an ampacity of ~150A, so double bars are needed to achieve a C1 rate for these cells.



1596722927717.png
 
1) never coat the threads, it acts like a grease and will skew pressure/force readings and possibly lead to stripping the soft aluminium.
2) you can buy Stainless screws that fit from Homedepot, while there, get matching stainless washers. Take your original screw to make sure you match thread etc perfectly. Don't wanna cross-thread now do you.
3) do NOT use Zinc Plated screws or hardware.

The Busbar that crosses from one cell set to the other (you show in a square block) are longer than those supplied, you will have to make your own with copper bar stock.

My cuts for 2X 24/280AH Block packs were as shown:
2x 4.250", for crossing between "sides"
12x 3.750" for between the cells themselves.
Material used: COPPER C110 FLAT BAR ASTM-B133 0.125" x 0.750"
This is 4mm thick more or less, works out perfect.
 
ok... makes sense.
I actually have a big problem now. And it was by using the original screws... I stripped at least two battery poles... the thread is gone :(
It started by noticing the busbar was hot. The contact resistance was high, so I raised the torque. It got better, but not enough. I continued raising torque and now the hole cannot hold the M6 screw...:(

Are there any photos of the inside of the cell, namely the aluminium posts? The top diameter is the same all the way down? How much alumininum is really there, both diagonally and downwards?
I need now to use bigger screews, but I don't imagine there are M7 available, are there?
For another build, I'm gonna buy some (expensive) aluminium bolts...
 
elimac_pt said:
ok... makes sense.
I actually have a big problem now. And it was by using the original screws... I stripped at least two battery poles... the thread is gone :(
It started by noticing the busbar was hot. The contact resistance was high, so I raised the torque. It got better, but not enough. I continued raising torque and now the hole cannot hold the M6 screw...:(

Are there any photos of the inside of the cell, namely the aluminium posts? The top diameter is the same all the way down? How much alumininum is really there, both diagonally and downwards?
I need now to use bigger screews, but I don't imagine there are M7 available, are there?
For another build, I'm gonna buy some (expensive) aluminium bolts...
Click to expand...
You can try and find helicoil in 6mm. They are stainless steel spirals that use a special size tape then you insert them and now you have a SS thread. I used Permatex Red with studs so I could take them to the bottom and a half turn out. That way I know I am getting the full length of the hole no mater the thickness of my straps and ring terminals. In many places I used double straps so having a variety of bolt lengths would be a pain.
 
I'm thinking about using helicoil for M5. This way I wouldn't have to dril. The outside dimensions should almost fit ok in a M6 threaded aluminium hole of the battery pad. What do you think?
 
M7 is extremely uncommon; the proper solution is what @Ampster said: a helicoil ;)

And use studs (or just longer bolts as studs), less chance of that happening again.

elimac_pt said:
I actually have a big problem now. And it was by using the original screws... I stripped at least two battery poles... the thread is gone :(
It started by noticing the busbar was hot. The contact resistance was high, so I raised the torque. It got better, but not enough. I continued raising torque and now the hole cannot hold the M6 screw...:(
Click to expand...

That's not normal. Did you sand and then cleaned the top of the terminal and the busbar just before assembly? are the busbar flat? burr free? big enough?
 
elimac_pt said:
The outside dimensions should almost fit ok in a M6 threaded aluminium hole of the battery pad. What do you think?
Click to expand...
I wouldn't go with an "almost fit" solution. Drill it out and tap it and you will get something that will handle the torque.
By the way, as @BiduleOhm said, to ensure good contacts on high Amp battery posts I use abrasive pad to get rid of oxide and then use NoAlox or similar anti oxidant to be sure I don't have problems.
 
I did clean the surface. The root cause is almost for sure that the copper bus bars are not 100% flat, thus the contact is not perfect and highly dependent on vertical force. And some of them were 100% cold, and some very hot. So, I did have good contacts in some cells. While in load, I also could measure the actual voltage drop between alu pads and copper bar. Huge differences in some cells!

I was watching some laminated copper busbars that, being slimer, could improve the situation. Or use some aluminium busbar (softer metal) in paralel, below the copper one. But I may not use this approach, I may very well go with the helicoil (never used them before).

After I receive both M6 and M5 helicoils I will see which one I use. I've seen there are M5x0.85x1D or M6x1x1D. I ordered both. Your advice and comments are extremely useful to begin forming an educated opinion!
 
Ok, so what I'd recommend is to sand the busbar on some sandpaper stuck on a flat surface (piece of glass for example) until it's flat ;)

Use M6, cancel your M5 order as it'll be too small.
 
I have received three different types of buss bars from two battery vendors and they were all different. I started making my own especially on the end positive and negative ones because there were so many other sensor wires connected to those two pairs. I made those out of 1/4 aluminum. In my 2P16S pack the ends are two battery terminals and I made extra holes so I don't have to loosen the battery post bolts to adjust other connections. You can see those on the left of the photo. The reason I like studs is each one goes all the way to the bottom so I know I have maximum number of threads for pullout strength, regardless of the thickness of the buss bars, lugs or ring terminals 20200809_082022.jpg
 
If the contact surface is in question, a bit of machinists blueprint compound (prussian blue) as a guide, and a coarse/medium stone should make short work of any high/low spots.
 
Has anyone considered making cable bridges with copper lugs?
For who is worried anout stripping the fragile aluminium threads, the flexible cable (35mm2 in my case) will help diminuish the strain on the poles. The busbars are too rigid.

If one disposes the prismatic cells back to back along the small side, the poles will dist a little more from each other, making more easy such a solution. For 8 cells, I will have 2 rows, making the main (-) and (+) appear at same side. Bridges will have ~9cm from centre holes.

There is another solution, dispose cells side by side on long side, all same direction, and connect in "Z" style. Bridges will be even longer, makins even less stress.
 
Nothing wrong with well crimped lugs and cable. You need to choose a lug with a good flat bottom, or sand it flat yourself. As you won't get a whole lot of clamping force with the small fastener.
 
I can confirm that well crimped lugs and 25mm2 cable resulted in with a much better interconnections than with the provided busbar (40mm2).
If we can't flat it out, better to not use them

Interconnection bridge from center ALU battery to the next, voltage drop while charging with 50A:
- Busbars: anything between 10mV and 30mV, depending on the connection/ pressure.
- 25/6 lug + 6cm 25mm2 cable, 9cm between lug m6 conection points: only 3mV, consistent in 4 tested bridges.

I whish I could have used 35mm2, but it would become even harder to build such short bridge cables, and we would lose some important flexibility, which is what the busbars lack.
 
Steve_S said:
Torque etc info can be found above.
A note on using noalox or similar. That is used on the surfaces between the cell contact face & busbar, not on the bolt threads. Only a very thin coating is used, no gobs of the stuff. The bolts & busbars as supplied by the various vendor can be different, usually, the busbars are copper (sometimes tin plated which is better) with stainless screws or bolts. If you get tin plated bus bars then you don't need noalox, obviously.
Click to expand...
Personally, I'm going to use noalox, since it's purpose is to prevent oxidation of aluminum (in particular when used as an electrical connection between aluminum and a dissimilar metal, like nickel or tin plated copper). You are correct that a thin film is all that is required. In many locations its use is required by code. What I'm trying to say, the product was designed for specifically the application most of us use it for. It is not locktite, and of course shouldn't be used as such (as you point out). I'm just trying to point out that it is specifically designed for the application, since most batteries we are purchasing (the aluminum cells with aluminum electrical contacts) are indeed connecting aluminum with a copper busbar (plated or not). Corrosion/oxidation of aluminum making a bad electrical connection doesn't depend on nickel or tin plated busbars, or even pure copper.
 
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Are 'brass' lugs acceptable when connecting the very thin balance wires. I've spotted ones that will allow me to get a really good connection and have a larger surface area for contact? Any real downsides to using brass, for the BMS balance wires?
 
Also of note, i'm sure i read somewhere(cant find it now:() that doubling up the xuba supplied busbars does not double up the ampacity, but gets you in the region of 175A.
Anyone care to confirm this?
You end up with so many nuggets of info on these threads, you lose track of them:cry:
 
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